And 2012 was also "a historic year for extreme weather that included drought, wildfires, hurricanes and storms," the data center points out. It notes, though, that "tornado activity was below average."

The center's "U.S. Climate Extremes Index" indicates that 2012 was "the second most extreme year on record for the nation. The index, which evaluates extremes in temperature and precipitation, as well as landfalling tropical cyclones, was nearly twice the average value and second only to 1998. ... 2012 [saw] 11 disasters that have reached the $1 billion threshold in losses, to include Sandy, Isaac, and tornado outbreaks experienced in the Great Plains, Texas and Southeast/Ohio Valley."

"Federal scientists said that the data were compelling evidence that climate change is affecting weather in the United States and suggest that the nation's weather is likely to be hotter, drier and potentially more extreme than it would have been without the warmer temperatures.

"Last year's record temperature is 'clearly symptomatic of a changing climate,' said Thomas R. Karl, who directs NOAA's National Climatic Data Center. Americans can now see the sustained warmth over the course of their own lifetimes — 'something we haven't seen before.' He added, 'That doesn't mean every season and every year is going to be breaking all-time records, but you're going to see this with increasing frequency.' "

"October was the only cooler than average month in the Lower 48 states in 2012. March and July were the warmest such months on record, there. Four other months: January (4th warmest), April (3rd warmest), May (2nd warmest) and June (8th warmest) landed in the top 10 warmest respective months."